1. Field of the Invention
The present invention relates to a vehicle speed control device that controls the speed of a vehicle within an object zone. Specifically, the present invention is directed to a vehicle speed control device which determines a target speed, based on map information and on a current location of a vehicle, and supplies the determined target speed to its speed controller. In addition, the present invention pertains to a method of setting a target speed of a vehicle by using the device and to program for executing the method.
2. Description of the Related Art
In order to control the speed of vehicles, many control devices (thereinafter called “vehicle speed control devices”) have been proposed. These control devices are designed to control the speed of a vehicle within a predetermined zone by using positioning means such as map information or a global positioning system (GPS). To give some examples, Japanese Unexamined Patent Application Publication 2005-178704 discloses a cruise-assist system, which is adapted to determine the target speed of a vehicle, based on the conditions of a route and by using a car navigation system (see paragraphs 0012 to 0018 and FIG. 3). Furthermore, Japanese Unexamined Patent Application Publication 2003-80970 discloses a vehicle speed control device, which is configured to determine the upper and lower limits of target speed of a vehicle, based on a speed desired by the driver and by using a GPS. Subsequently, this device executes an automatic cruising control (ACC), based on the predetermined upper and lower limits (see paragraphs 0004 to 0006 and FIG. 1).
In such control, it is preferable that a control device does not make a driver feel uncomfortable.
Japanese Unexamined Patent Application Publication 8-268109 discloses a vehicle speed control device, which is designed to keep measuring a rate at which the driver changes the speed of a vehicle. Then, the device adjusts the speed in compliance with the measured rate (see paragraphs 0006 to 0013 and FIG. 1). Moreover, Japanese Unexamined Patent Application Publication 10-100737 discloses a vehicle speed control device, which is adapted to determine a time period required for acceleration or deceleration by using infrastructure facilities such as beacons and based on a target speed at a predetermined point. Subsequently, the device changes the acceleration or deceleration continuously, thereby changing the speed of a vehicle smoothly (see paragraphs 0005 to 0008 and FIG. 1).
Japanese Unexamined Patent Application Publication 2005-297855 discloses a deceleration control device, which is configured to determine the target deceleration of a vehicle, based on an input travel orientation and driver's technique. Then, the device controls the speed of the vehicle, based on the predetermined deceleration (see paragraphs 0008 to 0011 and FIG. 1). In addition, Japanese Unexamined Patent Application Publication 2005-297621 discloses an automatic control device, which is adapted to automatically control the speed of a vehicle without making a driver feel uncomfortable. This device memorizes and learns the acceleration or deceleration patterns for each route and, then controls the speed of a vehicle based on the learned patterns when the vehicle runs on the same route (see paragraphs 007 to 0032 and FIG. 10).
In controlling the speed of a vehicle by using map information and a positioning means, it is difficult for a control device to determine the coordinates of a target point precisely. This is because the data acquired from a positioning means contains a considerable error.
Furthermore, after acquiring data from a positioning means, the device must correct the location coordinates of the vehicle by mapping the acquired data on the running route of the map information. In this case, if the acquired data is quite different from the current location coordinates, the current location may jump on the map information. Accordingly, the vehicle may pass through a target point, or changes its speed rapidly. This gives the driver an inconvenience or makes him or her feel uncomfortable.
Taking the above disadvantage into account, the present invention has been conceived. An object of the present invention is to provide a vehicle speed control device, which presents a driver with comfortable drive without causing the rapid speed change or by preventing a vehicle from unconsciously passing through a target point. Specifically, the vehicle speed control device is adapted to predict the rapid change in a target speed of a vehicle, and then, to change the speed of the vehicle more gradually than the target speed. An additional object of the present invention is to provide a method of setting a target speed of a vehicle by using the above device. Another object of the present invention is to provide a program for executing the above method.